Thermal storage device for use in a fluid flow system

ABSTRACT

An exhaust system is provided that includes at least one exhaust aftertreatment unit provided in an exhaust fluid flow pathway and a thermal storage device disposed upstream from the exhaust aftertreatment unit. The thermal storage device is operable to store thermal mass and provide thermal insulation to enable a catalyst to maintain a minimum predetermined temperature for a minimum predetermined time. In one form, a heater is also provided proximate the thermal storage device, along with variations that include a secondary flow pathway for the thermal storage device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. provisional application Ser. No. 62/302,482, filed on Mar. 2, 2016, the contents of which are incorporated herein by reference in their entirety. This application is also related to co-pending applications titled “Bare Heating Elements for Heating Fluid Flows,” “Virtual Sensing System,” “Advanced Two-Wire Heater System for Transient Systems,” “Heater Element Having Targeted Decreasing Temperature Resistance Characteristics,” “System for Axial Zoning of Heating Power,” “Dual-Purpose Heater and Fluid Flow Measurement System,” “Heater-Actuated Flow Bypass,” and “Susceptor for Use in a Fluid Flow System,” concurrently filed herewith and commonly assigned with the present application, the contents of which are incorporated herein by reference in their entirety.

FIELD

The present disclosure relates to heating and sensing systems for fluid flow applications, for example vehicle exhaust systems, such as diesel exhaust and aftertreatment systems.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

The use of physical sensors in transient fluid flow applications such as the exhaust system of an engine is challenging due to harsh environmental conditions such as vibration and thermal cycling. One known temperature sensor includes a mineral insulated sensor inside a thermowell that is then welded to a support bracket, which retains a tubular element. This design, unfortunately, takes a long amount of time to reach stability, and high vibration environments can result in damage to physical sensors.

Physical sensors also present some uncertainty of the actual resistive element temperature in many applications, and as a result, large safety margins are often applied in the design of heater power. Accordingly, heaters that are used with physical sensors generally provide lower watt density, which allows a lower risk of damaging the heater at the expense of greater heater size and cost (same heater power spread over more resistive element surface area).

Moreover, known technology uses an on/off control or PID control from an external sensor in a thermal control loop. External sensors have inherent delays from thermal resistances between their wires and sensor outputs. Any external sensor increases the potential for component failure modes and sets limitations of the any mechanical mount to the overall system.

One application for heaters in fluid flow systems is vehicle exhausts, which are coupled to an internal combustion engine to assist in the reduction of an undesirable release of various gases and other pollutant emissions into the atmosphere. These exhaust systems typically include various after-treatment devices, such as diesel particulate filters (DPF), a catalytic converter, selective catalytic reduction (SCR), a diesel oxidation catalyst (DOC), a lean NO_(x) trap (LNT), an ammonia slip catalyst, or reformers, among others. The DPF, the catalytic converter, and the SCR capture carbon monoxide (CO), nitrogen oxides (NO_(x)), particulate matters (PMs), and unburned hydrocarbons (HCs) contained in the exhaust gas. The heaters may be activated periodically or at a predetermined time to increase the exhaust temperature and activate the catalysts and/or to burn the particulate matters or unburned hydrocarbons that have been captured in the exhaust system.

The heaters are generally installed in exhaust pipes or components such as containers of the exhaust system. The heaters may include a plurality of heating elements within the exhaust pipe and are typically controlled to the same target temperature to provide the same heat output. However, a temperature gradient typically occurs because of different operating conditions, such as different heat radiation from adjacent heating elements, and exhaust gas of different temperature that flows past the heating elements.

The life of the heater depends on the life of the heating element that is under the harshest heating conditions and that would fail first. It is difficult to predict the life of the heater without knowing which heating element would fail first. To improve reliability of all the heating elements, the heater is typically designed to be operated with a safety factor to reduce and/or avoid failure of any of the heating elements. Therefore, the heating elements that are under the less harsh heating conditions are typically operated to generate a heat output that is much below their maximum available heat output.

SUMMARY

In one form of the present disclosure, an exhaust system is provided that comprises at least one exhaust aftertreatment unit provided in an exhaust fluid flow pathway and a thermal storage device disposed upstream from at least one exhaust aftertreatment unit, wherein the thermal storage device is operable to store thermal mass and provide thermal insulation to enable a catalyst to maintain a minimum predetermined temperature for a minimum predetermined time.

In another form, a secondary flow pathway in fluid communication with the exhaust fluid pathway is provided, wherein the thermal storage device is disposed within the secondary flow pathway. Further, a heater may be provided that is disposed proximate the secondary flow pathway and a flow control device actuated by the heater, wherein the flow control device is in communication with the secondary flow pathway.

In still another form, an exhaust system is provided that comprises at least one exhaust aftertreatment unit provided in an exhaust fluid flow pathway, a thermal storage device disposed upstream from at least one exhaust aftertreatment unit, and a heater disposed proximate the thermal storage device. The thermal storage device is operable to store thermal mass and provide thermal insulation to enable a catalyst to maintain a minimum predetermined temperature for a minimum predetermined time.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is schematic diagram of a diesel engine and exhaust aftertreatment system in which the principles of the present disclosure are applied;

FIG. 2 a schematic diagram of one form of a thermal storage device according to the teachings of the present disclosure; and

FIG. 3 is a schematic diagram of another form of a thermal storage device according to the teachings of the present disclosure.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

Referring to FIG. 1, an exemplary engine system 10 generally includes a diesel engine 12, an alternator 14 (or generator in some applications), a turbocharger 16, and an exhaust aftertreatment system 18. The exhaust aftertreatment system 18 is disposed downstream from the turbocharger 16 for treating exhaust gases from the diesel engine 12 before the exhaust gases are released to atmosphere. The exhaust aftertreatment system 18 can include one or more additional components, devices, or systems operable to further treat exhaust fluid flow to achieve a desired result. In one form, the exhaust aftertreatment system 18 includes a heating system 20, a diesel oxidation catalyst DOC 22, a diesel particulate filter device DPF 24, and a selective catalytic reduction device SCR 26. The heating system 20 includes a heater assembly 28 disposed upstream from the DOC 22, and a heater control device 30 for controlling operation of the heater assembly 28. The exhaust aftertreatment system 18 further includes an upstream exhaust conduit 32 that receives the heater assembly 28 therein, an intermediate exhaust conduit 34 in which the DOC 22 and DPF 24 are received, and a downstream exhaust conduit 36 in which the SCR is disposed. Although a diesel engine 12 is shown, it should be understood that the teachings of the present disclosure are also applicable to a gasoline engine and other fluid flow applications. Therefore, the diesel engine application should not be construed as limiting the scope of the present disclosure.

The DOC 22 is disposed downstream from the heater assembly 28 and serves as a catalyst to oxide carbon monoxide and any unburnt hydrocarbons in the exhaust gas. In addition, The DOC 22 converts nitric oxide (NO) into nitrogen dioxide (NO₂). The DPF 24 is disposed downstream from the DOC 22 to remove diesel particulate matter (PM) or soot from the exhaust gas. The SCR 26 is disposed downstream from the DPF 24 and, with the aid of a catalyst, converts nitrogen oxides (NOx) into nitrogen (N₂) and water. A urea water solution injector 27 is disposed downstream from the DPF 24 and upstream from the SCR 26 for injecting urea water solution into the stream of the exhaust gas. When urea water solution is used as the reductant in the SCR 18, NOx is reduced into N₂, H₂O and CO₂.

It should be understood that the engine system 10 illustrated and described herein is merely exemplary, and thus other components such as a NO_(x) adsorber or ammonia oxidation catalyst, among others, may be included, while other components such as the DOC 22, DPF 24, and SCR 26 may not be employed. Further, although a diesel engine 12 is shown, it should be understood that the teachings of the present disclosure are also applicable to a gasoline engine and other fluid flow applications. Therefore, the diesel engine application should not be construed as limiting the scope of the present disclosure. Such variations should be construed as falling within the scope of the present disclosure.

Referring to FIG. 2, an exhaust aftertreatment system according to the teachings of the present disclosure is illustrated and generally indicated by reference numeral 50. The exhaust aftertreatment system 50 generally includes an exhaust treatment unit 52, such as by way of example a selective catalyst reduction unit (SCR). The exhaust treatment unit 52 may be another type of unit, such as a catalytic converter, a diesel particulate filter, a diesel oxidation catalyst, a lean nitrogen oxides (NOx) trap, an ammonia slip catalyst, reformers, a decomposition tube, among others, and combinations thereof.

As shown, the exhaust aftertreatment system 50 further comprises a thermal storage device 54 disposed upstream from the exhaust treatment unit 52. This thermal storage device 54 is generally any device that can store heat or thermal mass, thereby providing “inertia” against temperature fluctuations. The thermal storage device 54 can store heat upstream of the exhaust aftertreatment unit 52 at a predetermined temperature for a predetermined time. More specifically, the thermal storage device is operable to store thermal mass and provide thermal insulation to enable a catalyst to maintain a minimum predetermined temperature for a minimum predetermined time. In one form, the minimum predetermined temperature is approximately 100° C. and the minimum predetermined time is about 8 hours. In another form, the minimum predetermined temperature is approximately 180° C. and the minimum predetermined time is a time span for an FTP-75 (Federal Test Procedure 75) test procedure. Accordingly, the time span and temperatures are across a cold start transient phase, a stabilized phase, a hot soak phase between, and then a hot start transient phase.

As further shown, in another form, at least one heater 56 is disposed proximate the thermal storage device 54. In one example, the thermal storage device 54 is a DPF (diesel particulate filter). In this exemplary form, during a preceding regeneration cycle, the thermal storage device 54 or thermal mass can store large thermal energy when the surroundings are higher in temperature than the mass. When the regeneration cycle is off, the thermal storage device 54 or thermal mass releases the thermal energy gradually when the surrounding temperature is lower than the thermal storage device 54 or thermal mass. Therefore, the thermal storage device 54 can help retain the heat and thus prolongs the regeneration cycle even after the heater 56 is turned off. The thermal storage device 54 is also operable to release thermal energy when the heater 56 is turned off and when the fluid temperature surrounding the thermal storage device 54 is lower than the temperature of the thermal storage device.

The thermal storage device 54 is made of a material that has excellent thermal mass (or thermal capacitance, or heat capacity), which refers to the ability of a body to store thermal energy. If the exhaust aftertreatment unit 52 is a DOC, the thermal storage device 54 can assist with light-off or NO to NO₂ conversion. If the exhaust aftertreatment unit 52 is an SCR, the thermal storage device 54 could assist with NO_(x) conversion. If the exhaust aftertreatment unit 52 is a decomposition tube upstream of an SCR, then the thermal storage device 54 could assist with processing of urea and with NO_(x) conversion in the decomposition tube.

The thermal storage device 54 may be in the form of a thermal flywheel as shown in FIG. 2. The thermal storage device 54 or thermal flywheel may also include a phase change material, an in one form a phase change material that changes phase at a temperature between 180° C. and 45° C.

Optionally, the thermal storage device 54 may be combined with a thermal insulator (not shown). The combination of heat storage capacity and thermal insulation enables at least one catalyst in the system to remain at a predetermined temperature for a predetermined time resulting in the warm-up period to be reduced or eliminated.

Referring now to FIG. 3, in another form, the thermal storage device 54 is positioned in a second fluid flow channel 58 that receives and warms the exhaust gas at times the exhaust gas temperature is low and would otherwise reduce the effectiveness of a catalyst in the exhaust gas flow. This exhaust system 60 further includes a fluid flow control device 62 that causes fluid to flow through the second fluid flow channel when actuated by the heater 56. Accordingly, when a heater 56 is turned on, the fluid flow control device 62 is actuated and causes the fluid to flow through the second fluid flow channel 58. Such heater-actuated flow device may be one of the various forms disclosed in copending application entitled “Heater-Actuated Flow Bypass,” which is commonly assigned with the present application and the contents of which are incorporated herein by reference in their entirety. Alternatively, the second fluid flow channel 58 may cool the exhaust gas at times when the exhaust gas temperature is high (or above a predetermined temperature) and would otherwise reduce the effectiveness of a catalyst in the exhaust gas flow.

In yet another form, the thermal storage device 54 may be disposed within the first fluid flow channel or within both the first fluid flow channel and second fluid flow channel.

The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure. 

What is claimed is:
 1. An exhaust system comprising: at least one exhaust aftertreatment unit provided in an exhaust fluid flow pathway; and a thermal storage device disposed upstream from the at least one exhaust aftertreatment unit, wherein the thermal storage device is operable to store thermal mass and provide thermal insulation to enable a catalyst to maintain a minimum predetermined temperature for a minimum predetermined time.
 2. The exhaust system according to claim 1, wherein the minimum predetermined temperature is approximately 100° C. and the minimum predetermined time is about 8 hours.
 3. The exhaust system according to claim 1, wherein the minimum predetermined temperature is approximately 180° C. and the minimum predetermined time is a time span for an FTP-75 test procedure.
 4. The exhaust system according to claim 3 further comprising a heater disposed proximate the thermal storage device.
 5. The exhaust system according to claim 4, wherein the thermal storage device is operable to release thermal energy when the heater is turned off and when the fluid temperature surrounding the thermal storage device is lower than the temperature of the thermal storage device.
 6. The exhaust system according to claim 1, wherein the at least one exhaust aftertreatment unit is selected from the group consisting of a catalytic converter, a diesel particulate filter, a selective catalytic reduction, a diesel oxidation catalyst, a lean nitrogen oxides (NOx) trap, an ammonia slip catalyst, reformers, a decomposition tube, and combinations thereof.
 7. The exhaust system according to claim 6, wherein the thermal storage device is operable to assist with at least one of light-off and NO to NO₂ conversion in the diesel oxidation catalyst unit.
 8. The exhaust system according to claim 6, wherein the thermal storage device is operable to assist with NOx conversion in the selective catalytic reduction unit.
 9. The exhaust system according to claim 6, wherein the decomposition tube is disposed upstream of a selective catalytic reduction unit.
 10. The exhaust system according to claim 9, wherein the thermal storage device is operable to assist with at least one of processing urea and NOx conversion in the decomposition tube.
 11. The exhaust system according to claim 1 further comprising a secondary flow pathway in fluid communication with the exhaust fluid pathway, wherein the thermal storage device is disposed within the secondary flow pathway.
 12. The exhaust system according to claim 11 further comprising a heater disposed proximate the secondary flow pathway and a flow control device actuated by the heater, wherein the flow control device is in communication with the secondary flow pathway.
 13. The exhaust system according to claim 12, wherein the heater is disposed proximate the thermal storage device.
 14. The exhaust system according to claim 11, wherein the secondary flow pathway functions to cool a flow of exhaust fluid when the exhaust fluid is above a predetermined temperature.
 15. The exhaust system according to claim 1, wherein the thermal storage device comprises a phase change material.
 16. The exhaust system according to claim 15, wherein the thermal storage device changes phase between a temperature of approximately 180° C. and 450° C.
 17. An exhaust system comprising: at least one exhaust aftertreatment unit provided in an exhaust fluid flow pathway; a thermal storage device disposed upstream from the at least one exhaust aftertreatment unit, wherein the thermal storage device is operable to store thermal mass and provide thermal insulation to enable a catalyst to maintain a minimum predetermined temperature for a minimum predetermined time; and a heater disposed proximate the thermal storage device.
 18. The exhaust system according to claim 17, wherein the thermal storage device is operable to release thermal energy when the heater is turned off and when the fluid temperature surrounding the thermal storage device is lower than the temperature of the thermal storage device.
 19. The exhaust system according to claim 17 further comprising a secondary flow pathway in fluid communication with the exhaust fluid pathway, wherein the thermal storage device is disposed within the secondary flow pathway.
 20. The exhaust system according to claim 17, wherein the thermal storage device comprises a phase change material that changes phase between a temperature of approximately 180° C. and 450° C. 